Changes in Phytoplankton Biomass and Nutrient Quantities in Sea Ice as Responses to Light/Dark Manipulations during different Phases of the Baltic Winter 2003 |
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Authors: | Janne-Markus Rintala Jonna Piiparinen Jens Ehn Riitta Autio Harri Kuosa |
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Institution: | 1. Tv?rminne Zoological Station, University of Helsinki, FI-10900, Hanko, Finland 2. Finnish Institute of Marine Research, P.O. Box 33, FI-00931, Helsinki, Finland 3. Division of Geophysics, Department of Physical Sciences, University of Helsinki, P.O. Box 64 FIN-00014, Finland 4. Centre for Earth Observation Science, University of Manitoba, Winnipeg, Manitoba, Canada
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Abstract: | The response of Baltic Sea ice communities to changing light climate was studied in three subsequent 3 week in situ experiments on the SW coast of Finland. The investigation covered three different winter periods, short day with low solar
angles leading to limited light in the ice, late winter with deep snow cover and early spring with melting snow and increasing
light availability. The experimental setup consisted of transparent (no snow) and completely darkened (heavy snow cover) plexiglass
tubes in which the ice cores were incubated in situ from 1 to 2 weeks. Changes in the concentrations of inorganic nutrients (NO3−-–N, PO43−-–P, SiO4−-–Si) and chlorophyll-a concentration in the phytoplankton community composition were recorded as responses to different light manipulations. Changes
in inner ice light intensity in untreated ice as well as the temperature both in air and ice were recorded over the entire
study period. Increased irradiance in late winter/early spring and during meltdown affected the chlorophyll-a amount in the sea ice. During these periods the phytoplankton community in the top layers decreased possibly as a consequence
of photo-acclimation. Closer to the bottom of the ice, however, the increased inner ice light intensity induced algal growth.
Complete exclusion of light stopped the algal growth in the whole ice column. Darkening the ice cores also slowed down the
ice melting opposite to accelerated melting caused by increased light. The significant differences found in nutrient concentrations
between the light and dark treatments were mostly explicable by changes in algal biomass. No obvious changes were observed
in the phytoplankton community composition due to light manipulation, diatoms and heterotrophic flagellates dominating throughout
the study period. |
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Keywords: | Baltic Sea ice ice biota chlorophyll-a inner ice light milieu |
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